Carcinogenic benzene levels peak in Delhi

Petrol pumps and heavy traffic locations worst affected

By Anumita Roychowdhury
Published: Thursday 15 March 2012

imageAlarmingly high levels of benzene have been reported in Delhi’s air. The levels in some areas like around IGI airport and Civil Lines, exceed the annual standard of 5 microgramme per cubic metre by 2 to 5 times. This is extremely worrying as benzene—a volatile compound of petrol—is a toxic air pollutant and a potent carcinogen. It can be extremely harmful even at trace amounts. Being volatile, it also contributes towards formation of yet another harmful gas, ozone.

The available evidences from Delhi Pollution Control Committee (DPCC) point towards benzene hotspots in heavy traffic locations in the city (see Graph 1: High benzene levels in heavy traffic locations of Delhi). Independent studies carried out by scientists at the Jawaharlal Nehru University during two different time periods—2001 and 2002 and winter months of 2007—also showed an increase in benzene levels in the city. The study also attributed the rise to increase in vehicular traffic in the city.

Graph 1: High benzene levels in heavy traffic locations of Delhi
Source: Based on data provided in DPCC’s real-time database

Apart from the increasing vehicular traffic, another major cause of worry is unacceptably high-concentrations of benzene in and around refuelling stations in Delhi. The Tata Energy Research Institute (TERI) has monitored benzene levels at 40 petroleum-filling stations in Delhi and within the breathing zone of the dispensing crew between 2009 and 2010. These sites include the fuel stations of Indian Oil, Hindustan Petroleum and Bharat Petroleum located in South Extension, Lodhi Road, Defence Colony, Vikas Marg, Connaught Place and Chanakyapuri. While an annual average of 5 microgramme per cum of benzene is allowed legally the actual recorded maximum concentration of this toxic group of compounds–benzene, xylene and toluene, is phenomenally high – 6,406, 5,890, and 9,512 microgramme per cum, respectively (See Graph 2: Maximum volatile organic compound levels (benzene, toluene, xylene) recorded in petrol pumps in 2009-10)

Graph 2: Maximum volatile organic compound levels (benzene, toluene, xylene) recorded in petrol pumps in 2009-10
Source: Meena Sehgal et al 2011, Variations in air quality at filling stations, Delhi, India, International Journal of Environmental Studies, 68:6, pages 845-849

Source: MoEF/CPCB 2011, Air quality monitoring, emission inventory and source apportionment study for Indian cities, National Summary report

Petrol is a highly volatile fuel and quickly evaporates during loading and dispensation. This makes the refuelling stations high-risk areas. Petrol pump workers, dealers and vehicle users are at serious risk of exposure. It’s not just Delhi, smaller cities like Bengaluru, Kanpur and Pune have reported even higher levels of benzene.  The peak levels in these cities are shocking.

The toxic risk

Benzene is a potent carcinogen and is blamed for leukemia. The WHO estimates a 4 in 1 million risk of leukemia on exposure to benzene to a concentration of 1μg/m3. Increased incidences of leukemia (cancer of the tissues that form white blood cells) have been observed in humans occupationally exposed to benzene.  Long-term inhalation can cause various disorders in the blood, including reduced numbers of red blood cells and aplastic anaemia, especially in occupational settings.  

There are some short-term effects as well. According to US Environmental Protection Agency exposure to benzene may cause drowsiness, dizziness, headaches, as well as eye, skin, and respiratory tract irritation, and, at high levels, unconsciousness. Women may suffer from reproductive effects if they are exposed to high-levels. T K Joshi, doctor at Maulana Azad Medical College in Delhi, says women are particularly vulnerable to benzene poisoning as it is a fat soluble toxin.

Improve fuel quality

Air-borne benzene comes from fuel vapourisation and evaporation and exhaust emissions from vehicles. Benzene and aromatic compounds occur naturally in petroleum and become more concentrated when petrol is refined to produce high octane gasoline. While the benzene content in petrol must be minimised, total aromatics must also be reduced because this also contributes towards formation of benzene.

India has taken steps to meet the international standards of 1 per cent benzene in petrol. In Bharat Stage IV petrol, currently available in major cities, the total aromatic content has been reduced to 35 per cent and olefins—unsaturated  chemical compound containing at least one carbon-to-carbon double bond and widely used in petrochemical industry—content to 18 per cent. But given the level of air-borne benzene in cities and rising level of vehicular traffic there is need for further control. The global best practice shows that benzene content–as in the US–is now 0.62 per cent and the aromatics 25 per cent in polluted areas.

Prevent evaporation

As petrol quickly evaporates and adds to the emissions, cities will require very stringent control on loss of fuel through evaporation. All refulling stations should be retrofitted with vapour recovery system that traps the petrol vapour and puts it back in the tank. (See Box: How other countries are reducing evaporative losses from refuelling stations?). This is needed while dispensing fuel to vehicles as well as at the storage tanks.

Moreover, petrol can also evaporate from motor vehicle tanks. Already evaporative standards have been set for cars. But such standards are yet to be enforced for two-and three-wheelers. This has already been done in small countries like Thailand. In India estimates of evaporative emissions from two-wheelers are not available in public domain. Global assessments have shown that motorcycles equipped with carburetor—a device that blends air and fuel for an internal combustion engine—emit about 1.2-1.3 kg hydrocarbons per year per vehicle.

Other countries like the US and Europe have taken further steps to equip the vehicles with on-board recovery of petrol vapour and to put it back in the tank. This is urgently needed in India as well to control evaporative losses from the vehicles.

To further reduce benzene emissions from vehicles India would need to make a quick transition to the next level of emissions standards. This will enable advanced technologies and emissions control systems. In the two-wheeler segment switch from old two-stroke engines to four-stroke engines has helped to lower the exhaust emissions significantly. However, all three-wheeler models petrol as well as gaseous fuel models need after treatments systems as well to scavenge the toxic emissions.

Fuel savings

Gross neglect of petrol emissions will not only add to the health risk but also compound fuel costs. At a time when petrol is so precious and expensive and energy security under threat, letting petrol evaporate through negligence will hurt all. This adds enormously to energy costs. Both petrol pump dealers as well as vehicle users need to be made aware that evaporative losses of petrol means direct fuel loss. It is estimated that 1,000 cubic metre of petrol vapour is equivalent to losing about a litre of petrol. This, therefore, makes eminent sense to capture  vapour and put it back in the tank to save fuel.  This will not only strengthen energy security but also reduce public health risks.

How other countries are reducing evaporative losses from refueling stations?
Stage I Petrol Vapour Recovery was designed to prevent emissions of volatile organic compounds during the storage of petrol at terminals and distribution to service stations. Terminals should have floating roofs and reflective coatings so as to reduce evaporative losses from storage tanks. In addition when petrol is loaded onto tankers and transported to service stations vapour is recovered and returned to the tanker or terminal. Similar measures are deployed for underground tanks
Stage II Petrol Vapour Recovery involves over and above the state I system the provision of recovering petrol vapour displaced from the fuel tank of a motor vehicle during refuelling at a service station and transferring that petrol vapour to an underground storage tank at the service station or back to the petrol dispenser for resale
United States
Vapour Recovery Stage 2 was first developed in California and mandated in 1973. The 1990 amendments to the US Clean Air Act mandated Vapour Recovery Stage 2 in areas that had not consistently met ozone standards across the US, for service stations with throughputs greater than 0.5 million litres of petrol a year. US rules designate a vapour-recovery efficiency of 95 per cent and require California Air Resources Board (CARB)-type approval of VR2 equipment
Vapour Recovery Stage 2 is currently in place in urban areas in 27 US States, and state-wide in six States. It was introduced at a national level from November 1993 in areas that had not consistently met ozone standards

Subscribe to Daily Newsletter :

Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.